Saturday 8 July 2023

Grey Water for my Red Roses

Its summertime in southern England!


So that means its water-shortage-time.

The challenge is to keep your precious plants alive while minimising the use of fresh water.

Grey water is basically waste water from our homes that does not include 'black water' (i.e. the waste from toilets). Typically, grey water is made up from the output of one or more of the following used water sources: bath, shower, sinks/basins, washing machines and dish washers.


On a recent trip to a garden centre, we noticed a small, 1000 litre water butt 'kit'. We wondered if this could be positioned in our side alley and coupled into the bathroom downpipe. Surely this would then store grey water for use on our plants during dry spells.

there may be a problem

It was only after we brought it home and fitted it that I took to the internet, searching for info on grey water use. The biggest potential problem seems to be storing your grey water.

The common message is that you must use grey water within 24 hours, or it will start to smell real bad! When I say common message, I mean that all the websites I found issuing a 'storage warning' use this 24 hour time limit. Suspicious? It probably means that this figure comes from a single source and that everyone else is just quoting it.

If so, this repetition does not make the statement any more valid ...just saying.

why not give it a go?

So we pushed ahead anyway. Armed with only the local weather forecast, we connected the water butt to the down-pipe on days when we knew it was unlikely to rain in the coming days, and disconnected the butt prior to wet periods, when the water was not needed. We normally use the grey water on the same day of 'manufacture' but sometimes a day or so after. This doesn't mean that the butt is fully emptied after each use, only that it stops coming out of the tap. In practice, there will always be a few litres of grey water and sludge sitting in the bottom.

So far, after several weeks of use, I can report that the butt does not smell bad. It just smells like, well, bath water. But I guess it could still be early days. If it does start to pong after a few months, I'll just fill it up with fresh water once or twice and then revert to using grey water once again. After (say) 3 months we should have a good idea if this simple 'grey water system' is workable.

Points to note

In our case we are only collecting grey water from a shower and small basin. So our grey water only contains diluted soap, shampoo, particles of skin & hair and a few pathogens. Therefore 'fermentation' may not be as active as it would be if we also collected water from the dishwasher and/or washing machine.

Our grey water will contain pathogens from both the shower use and washing hands in the basin. If your grey water feed is also connected to the washing machine, it will contain many more pathogens. And if also connected to the dish washer, food waste may promote fermentation, all adding to any 'bad smell' risk.

The build up of sludge will require dealing with from time to time (e.g. the butt may need to be properly washed out).

More internet info from the RHS (the Royal Horticultural Society) advises not to use grey water on any of your edible plants.

Long term use of grey water may be detrimental to some plants, but again this claim may need further examination (e.g. is my low-polluted grey water any better than if it contained dish & washing machine water?). In any case, as already mentioned, our grey water is not for long term use.

Using grey water may contravene local or national regulations in some countries (maybe even here in Bognor!)

how much water is collected?

Apparently a typical Brit uses about 50 litres on average per shower. I suspect I use more, but lets take; 50 x 2 people = 100 litres or about 26 gallons in old money. Even with a big 10L watering can, that's 10 can loads.


Our new house has a much smaller garden than our previous home, so is much more manageable.

In use, we only water pots, hanging baskets and a few newly planted plants with our grey water, and (at the moment) only for a few days when the weather forecast indicates a dry period. The real test for the plants will be if we get an extended dry period of several weeks; will any suffer from this murky ration?

In practice our 'grey water season' will be relatively short; maybe only 4 or 5 months each year.

We don't use water butts connected to our rain water gutters at our new house because ...we can't be arsed. Any gutter-butts would have to be either at the front or back (or both) of the house. They would look butt-ugly, whereas our grey water butt is hidden at the side of the house. In practice with gutter-butts, a few days into a dry period, you run out of rain water. Our grey system gives us water every day that the down pipe is connected.

Ideally I could do with a tap fitted in-line to the grey water takeoff pipe. This would save pulling the pipe off and tucking it higher behind the down pipe to stop water shooting out onto the path.

The ideal arrangement for us might be 2 butts in our side-alley linked together; one rain water connected to a gutter, the other grey water. Such a system would be self flushing during rainy periods, if we always took water from the grey butt before using the rain butt.

Unfortunately we don't have a convenient gutter/down-pipe at the side of the house.

The experiment continues!

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